STIX Version 1.2.1. Part 3: Core

STIXTM Version 1.2.1. Part 3: Core

Committee Specification 01

05 May 2016

Specification URIs

This version:

Previous version:

Latest version:

(Authoritative)

Technical Committee:

OASIS Cyber Threat Intelligence (CTI) TC

Chair:

Richard Struse (), DHS Office of Cybersecurity and Communications (CS&C)

Editors:

Sean Barnum (), MITRE Corporation

Desiree Beck (), MITRE Corporation

AharonChernin (), Soltra

Rich Piazza (), MITRE Corporation

Additional artifacts:

This prose specification is one component of a Work Product that also includes:

STIX Version 1.2.1. Part 1: Overview.
STIX Version 1.2.1. Part 2: Common.
STIX Version 1.2.1. Part 3: Core (this document).
STIX Version 1.2.1. Part 4: Indicator.
STIX Version 1.2.1. Part 5: TTP.
STIX Version 1.2.1. Part 6: Incident.
STIX Version 1.2.1. Part 7: Threat Actor.
STIX Version 1.2.1. Part 8: Campaign.
STIX Version 1.2.1. Part 9: Course of Action.
STIX Version 1.2.1. Part 10: Exploit Target.
STIX Version 1.2.1. Part 11: Report.
STIX Version 1.2.1. Part 12: Default Extensions.
STIX Version 1.2.1. Part 13: Data Marking.
STIX Version 1.2.1. Part 14: Vocabularies.
STIX Version 1.2.1. Part 15: UML Model.
UML Model Serialization:

Related work:

This specification replaces or supersedes:

STIXTM 1.2 Core Specification (v1.2).

This specification is related to:

CybOXTM Version 2.1.1. Work in progress.
CybOXTM 2.1.

Abstract:

The Structured Threat Information Expression (STIX) framework defines nine core constructs and the relationships between them for the purposes of modeling cyber threat information and enabling cyber threat information analysis and sharing. This specification document defines the Core data model, which defines the STIX Package, the root object for all STIX content.

Status:

This document was last revised or approved by the OASIS Cyber Threat Intelligence (CTI) TCon the above date. The level of approval is also listed above. Check the “Latest version” location noted above for possible later revisions of this document. Any other numbered Versions and other technical work produced by the Technical Committee (TC) are listed at

TC members should send comments on this specification to the TC’s email list. Others should send comments to the TC’s public comment list, after subscribing to it by following the instructions at the “Send A Comment” button on the TC’s web page at

For information on whether any patents have been disclosed that may be essential to implementing this specification, and any offers of patent licensing terms, please refer to the Intellectual Property Rights section of the TC’s web page (

Citation format:

When referencing this specification the following citation format should be used:

[STIX-v1.2.1-Core]

STIXTM Version 1.2.1. Part 3: Core. Edited by Sean Barnum, Desiree Beck, AharonChernin, and Rich Piazza.05 May 2016. OASIS Committee Specification 01. Latest version:

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STIX™, TAXII™, AND CybOX™ (STANDARD OR STANDARDS) AND THEIR COMPONENT PARTS ARE PROVIDED “AS IS” WITHOUT ANY WARRANTY OF ANY KIND, EITHER EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, ANY WARRANTY THAT THESE STANDARDS OR ANY OF THEIR COMPONENT PARTS WILL CONFORM TO SPECIFICATIONS, ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR FREEDOM FROM INFRINGEMENT, ANY WARRANTY THAT THE STANDARDS OR THEIR COMPONENT PARTS WILL BE ERROR FREE, OR ANY WARRANTY THAT THE DOCUMENTATION, IF PROVIDED, WILL CONFORM TO THE STANDARDS OR THEIR COMPONENT PARTS. IN NO EVENT SHALL THE UNITED STATES GOVERNMENT OR ITS CONTRACTORS OR SUBCONTRACTORS BE LIABLE FOR ANY DAMAGES, INCLUDING, BUT NOT LIMITED TO, DIRECT, INDIRECT, SPECIAL OR CONSEQUENTIAL DAMAGES, ARISING OUT OF, RESULTING FROM, OR IN ANY WAY CONNECTED WITH THESE STANDARDS OR THEIR COMPONENT PARTS OR ANY PROVIDED DOCUMENTATION, WHETHER OR NOT BASED UPON WARRANTY, CONTRACT, TORT, OR OTHERWISE, WHETHER OR NOT INJURY WAS SUSTAINED BY PERSONS OR PROPERTY OR OTHERWISE, AND WHETHER OR NOT LOSS WAS SUSTAINED FROM, OR AROSE OUT OF THE RESULTS OF, OR USE OF, THE STANDARDS, THEIR COMPONENT PARTS, AND ANY PROVIDED DOCUMENTATION. THE UNITED STATES GOVERNMENT DISCLAIMS ALL WARRANTIES AND LIABILITIES REGARDING THE STANDARDS OR THEIR COMPONENT PARTS ATTRIBUTABLE TO ANY THIRD PARTY, IF PRESENT IN THE STANDARDS OR THEIR COMPONENT PARTS AND DISTRIBUTES IT OR THEM “AS IS.”

Table of Contents

1Introduction

1.1 STIXTM Specification Documents

1.2 Document Conventions

1.2.1 Fonts

1.2.2 UML Package References

1.2.3 UML Diagrams

1.2.4 Property Table Notation

1.2.5 Property and Class Descriptions

1.3 Terminology

1.4 Normative References

1.5 Non-Normative References

2Background Information

2.1 Component Data Models

2.1.1 Observable

2.1.2 Indicator

2.1.3 Incident

2.1.4 Tactics, Techniques and Procedures (TTP)

2.1.5 Campaign

2.1.6 Threat Actor

2.1.7 Exploit Target

2.1.8 Course of Action (COA)

2.1.9 Report

3STIXTM Core Data Model

3.1 STIXPackageVersionType Enumeration

3.2 STIXHeaderType Class

3.3 Content Aggregation Types

3.3.1 CampaignsType Class

3.3.2 CoursesOfActionType Class

3.3.3 IncidentsType Class

3.3.4 IndicatorsType Class

3.3.5 ThreatActorsType Class

3.3.6 TTPsType Class

3.3.7 ReportsType

3.4 RelatedPackagesType Class

3.4.1 RelatedPackageType Class

4Conformance

Appendix A. Acknowledgments

Appendix B. Revision History

stix-v1.2.1-cs01-part3-core05 May 2016

1Introduction

[All text is normative unless otherwise labeled]

The Structured Threat Information Expression (STIXTM) framework defines nine top-level component data models: Observable[i], Indicator, Incident, TTP, ExploitTarget, CourseOfAction, Campaign,ThreatActor, and Report. In addition, it defines a core data model for packaging and conveying content from any of these top-level components. This document serves as the specification for the STIX Core data model, which is the unifying data model for all STIX content.

The STIX Coredata model defines the concept of a STIX Package, the top-level object that is used to aggregate and convey all other objects of the STIX data models. The STIX Package has two main parts: a set of instances of any of the nine top-level components, which is the content of the STIX Package, and a STIX header, which can provide context for that content.

In Section 1.1 we discuss additional specification documents, in Section 1.2we provide document conventions, and in Section 1.3 we provide terminology. References are given in Sections 1.4 and 1.5. In Section 2, we give background information to help the reader better understand the specification details that are provided later in the document. We present the Core data model specification details in Section 3and conformance information in Section 4.

1.1STIXTM Specification Documents

The STIX specification consists of a formal UML model and a set of textual specification documents that explain the UML model. Specification documents have been written for each of the key individual data models that compose the full STIX UML model.

The STIX Version 1.2.1 Part 1: Overview document provides a comprehensive overview of the full set of STIX data models, which in addition to the nine data models mentioned in the Introduction, includes a core data model, a common data model, a cross-cutting data marking data model, various extension data models, and a set of default controlled vocabularies. STIX Version 1.2.1 Part 1: Overview also summarizes the relationship of STIX to other languages and outlines general STIX data model conventions.

Figure 11 illustrates the set of specification documents that are available. The color black is used to indicate the specification overview document, altered shading differentiates the overarching Core and Common data models from the supporting data models (vocabularies, data marking, and default extensions), and the color white indicates the component data models. The solid grey color denotes the overall STIX Language UML model. This STIX Core specification document is highlighted in its associated color (see Section 1.2.3.3). For a list of all STIX documents and related information sources, please see STIX Version 1.2.1 Part 1: Overview.

Figure 11. STIXTM Language v1.2.1 specification documents

1.2Document Conventions

The following conventions are used in this document.

1.2.1Fonts

The following font and font style conventions are used in the document:

Capitalization is used for STIX high level concepts, which are defined in STIX Version 1.2.1 Part 1: Overview.

Examples: Indicator, Course of Action, Threat Actor

The Courier New font is used for writing UML objects.

Examples: RelatedIndicatorsType, stixCommon:StatementType

Note that all high level concepts have a corresponding UML object. For example, the Course of Action high level concept is associated with a UML class named, CourseOfActionType.

The ‘italic’ font (withsingle quotes) is used for noting actual, explicit values for STIX Language properties. The italic font (without quotes) is used for noting example values.

Example: ‘PackageIntentVocab-1.0,’ high, medium, low

1.2.2UML Package References

Each STIX data model is captured in a different UML package (e.g., Core package, Campaign package, etc.). To refer to a particular class of a specific package, we use the format package_prefix:class, wherepackage_prefixcorresponds to the appropriate UML package. STIX Version 1.2.1 Part 1: Overviewcontains a list of the packages used by the Core data model, along with the associated prefix notations, descriptions, examples.

Note that in this specification document, we do not explicitly specify the package prefix for any classes that originate from the Coredata model.

1.2.3UML Diagrams

This specification makes use of UML diagrams to visually depict relationships between STIX Language constructs. Note that the diagrams have been extracted directly from the full UML model for STIX; they have not been constructed purely for inclusion in the specification documents. Typically, diagrams are included for the primary class of a data model, and for any other class where the visualization of its relationships between other classes would be useful. This implies that there will be very few diagrams for classes whose only properties are either a data type or a class from the STIX Common data model. Other diagrams that are included correspond to classes that specialize a superclass and abstract or generalized classes that are extended by one or more subclasses.

In UML diagrams, classes are often presented with their attributes elided, to avoid clutter. The fully described class can usually be found in a related diagram. A class presented with an empty section at the bottom of the icon indicates that there are no attributes other than those that are visualized using associations.

1.2.3.1Class Properties

Generally, a class property can be shown in a UML diagram as either an attribute or an association (i.e., the distinction between attributes and associations is somewhat subjective). In order to make the size of UML diagrams in the specifications manageable, we have chosen to capture most properties as attributes and to capture only higher level properties as associations, especially in the main top-level component diagrams. In particular, we will always capture properties of UML data types as attributes. For example, properties of a class that are identifiers, titles, and timestamps will be represented as attributes.

1.2.3.2Diagram Icons and Arrow Types

Diagram icons are used in a UML diagram to indicate whether a shape is a class, enumeration or data type, and decorative icons are used to indicate whether an element is an attribute of a class or an enumeration literal. In addition, two different arrow styles indicate either a directed association relationship (regular arrowhead) or a generalization relationship (triangle-shaped arrowhead). The icons and arrow styles we use are shown and described in Table 11.

Table 11. UML diagram icons

Icon / Description
/ This diagram icon indicates a class. If the name is in italics, it is an abstract class.
/ This diagram icon indicates an enumeration.
/ This diagram icon indicates a data type.
/ This decorator icon indicates an attribute of a class. The green circle means its visibility is public. If the circle is red or yellow, it means its visibility is private or protected.
/ This decorator icon indicates an enumeration literal.
/ This arrow type indicates a directed association relationship.
/ This arrow type indicates a generalization relationship.

1.2.3.3Color Coding

The shapes of the UML diagrams are color coded to indicate the data model associated with a class. The colors used in the Core specification are illustrated via exemplars in Figure 12. The overarching Core and Common data models, use the same light blue color coding.

Figure 12. Data model color coding

1.2.4Property Table Notation

Throughout Section 3, tables are used to describe the properties of each data model class. Each property table consists of a column of names to identify the property, a type column to reflect the datatype of the property, a multiplicity column to reflect the allowed number of occurrences of the property, and a description column that describes the property. Package prefixes are provided for classes outside of the Core data model (see Section 1.2.2).

Note that if a class is a specialization of a superclass, only the properties that constitute the specialization are shown in the property table (i.e., properties of the superclass will not be shown). However, details of the superclass may be shown in the UML diagram.

1.2.5Property and Class Descriptions

Each class and property defined in STIX is described using the format, “The X property verbY.” For example, in the specification for the STIX Indicator, we write, “The id property specifies a globally unique identifier for the kill chain instance.” In fact, the verb “specifies” could have been replaced by any number of alternatives: “defines,” “describes,” “contains,” “references,” etc.

However, we thought that using a wide variety of verb phrases might confuse a reader of a specification document because the meaning of each verb could be interpreted slightly differently. On the other hand, we didn’t want to use a single, generic verb, such as “describes,” because although the different verb choices may or may not be meaningful from an implementation standpoint, a distinction could be useful to those interested in the modeling aspect of STIX.

Consequently, we have chosen to use the three verbs, defined as follows, in class and property descriptions:

Verb / STIX Definition
captures / Used to record and preserve information without implying anything about the structure of a class or property. Often used for properties that encompass general content. This is the least precise of the three verbs.
Examples:
The Source property characterizes the source of the sighting information. Examples of details captured include identitifying characteristics, time-related attributes, and a list of the tools used to collect the information.
The Description property captures a textual description of the Indicator.
characterizes / Describes the distinctive nature or features of a class or property. Often used to describe classes and properties that themselves comprise one or more other properties.
Examples:
The Confidence property characterizes the level of confidence in the accuracy of the overall content captured in the Incident.
The ActivityType class characterizes basic information about an activity a defender might use in response to a Campaign.
specifies / Used to clearly and precisely identify particular instances or values associated with a property. Often used for properties that are defined by a controlled vocabulary or enumeration; typically used for properties that take on only a single value.
Example:
The version property specifies the version identifier of the STIX Campaign data model used to capture the information associated with the Campaign.

1.3Terminology

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC2119].